Gas analysis apparatus



May 2, 1950 w. M. ZAIKOWSKY 3 GAS ,mwzsxs APPARATUS Original Filed March1, 1943 2 Sheets-Sheet l Ha aii In an" a a. 21 I I a4) 1,, (2,3 11 Myaqlfoinzy May 2, 1950 Original Filed March 1, 194;

w. M. ZAIKOWSKY 2,506,535

GAS mwzsxs APPARATUS 2 sheets-sheet 2 I M/LADIMIR M ZA/KUWSKY PatentedMay 2, 1950 UNITED STATES PATENT OFFICE GAS ANALYSIS APPARATUS Originalapplication March 1, 1943, Serial No.

Divided and this application March 13, 1945, Serial No. 582,467

12 Claims. 1

This is a division of my copending application, Serial No. 477,675,filed March 1, 1943, and entitled Gas analyzer." The originalapplication discloses complete systems for gas analysis by measurementof thermal-conductivity, whereas this application discloses and claims aspecific cell block and associated apparatus that is particularly usefulin connection with the systems and methods claimed in the originalapplication but may also be useful in other systems.

An object of the present invention is'to provide apparatus that isparticularly effective in making measurements of thethermal-conductivities of gases at pressures diflerent from the ambientpressure.

Another object is to provide a construction of thermal-conductivity cellthat is simple and easy to construct.

Another object is to provide a thermal-conductivity cell assembly formeasuring thermalconductivity of gases at sub-ambient pressures thatdoes not require an elaborate sealing structure to prevent leakage ofatmospheric air into the cells and can be repeatedly disassembled andreassembled without introducing leakage.

Another object is to facilitate the accurate mounting of the filamentsin thermal-conductivity cells.

Another object is to provide a cell block construction forthermal-conductivity analysis that permits opening of the cell blockwithout disconnecting the gas connections and the electricalconnections.

Another object is to provide a cell capable of giving prompt andaccurate response to a change in gas composition over a wide range ofpressures.

Another object is to provide a construction that provides for theaccurate mounting, and the inspection, of resistors in a cell ofextremely small dimensions, to thereby facilitate manufacture ofapparatus in which the stability of zero and the sensitivity is to ahigh degree unaffected by variations in the pressure of the'gas undertest.

A feature of the invention is a cell structure in which one portion ofthe cell wall is incorporated in one member and the remaining portion ofthe cell wall is incorporated in a second member, the one membercontaining the gas connections to the cells and the other membercontaining the electrical connections to the cells, whereby the twomembers can be effectively produced as separate articles of manufacture.

Essentially the present invention comprises a cell structure consistingof two blocks that have registering recesses therein which define thecells when the blocks are bolted or otherwise clamped together. Thecells are preferably circular in cross sectional shape and are definedby recesses of semi-circular cross section in the two blocks. Thefilaments are supported in only one of the blocks (which may be thefront blocks) by insulated and hermetically sealed lead-ins that extendthrough the block to the exterior thereof. This permits ready assemblyand adjustment of the filament while the two blocks are separated. Thegas connections are preferably formed directly in the other block (whichmay be the rear block) so that the front block, carrying the filaments,can be removed for inspection, cleaning or repair without moving therear block from its installed position and, hence, without breaking thegas connections to the rear blocks. The auxiliary electrical apparatusthat is always used in conjunction with thermal-conductivity cells canbe conveniently mounted directly on the front block.

To prevent leakage of atmospheric air into the cells, a seal isnecessary between the abutting surfaces of the two blocks. In accordancewith the present invention, I eliminate the necessity of a perfect sealbetween the blocks by surrounding the cell recess in one of thev blockswith a groove which is connected to the gas passage. With thisarrangement the space defined by the groove is maintained at the same ora lower pressure than exists in the cells themselves, so that any airleaking between the blocks toward the cells will be trapped by thegroove and drawn off before it can reach the cell.

A full understanding of the invention may be had from the detaileddescription to follow, read in connection with the drawing, in which:

Fig. 1 is a schematic diagram of a system with which the apparatus ofthe present invention can be employed;

Fig. 2 is a perspective view with parts broken away, showing oneembodiment of the present invention;

Fig. 3 is a front elevational view of the apparatus shown in perspectivein Fig. 2;

Fig. 4 is a front elevation of the rear block of the apparatus shown inFig. 3; and

Fig. 5 is a vertical section taken along the line V-V of Fig. 4.

Referring to Fig. 1, there is shown a pipe II which contains a stream ofgas to be analyzed. A portion of this gas in conveyed through aconstriction II and conduit l2, thence through a valve l3 to a testpassage ll, from which it is one diagonal point of the bridge.

exhausted through an exhaust conduit [3 by a suction pump it. The testpassage i4 communicates through diffusion passages H with two test cellsl8 and I9, respectively, which contain resistors connected in diagonallyopposite arms of a bridge 29. The other arms of the bridge consistof-similar, resistors in test cells 2| and 22 which are connected bydiffusion passages to a reference passage 23, similar to the testpassage [4 but connected at its input end by a conduit 24 and arestrictor 25 to a source of reference gas in a pipe Illa, which gas inthis instance is atmospheric air. The output end of the referencepassage 23 communicates with the output end of the test passage I4 atthejunction 26.

The bridge 20 comprises, in addition to the resistors of the four testcells, a balancing potentiometer 21, the variable tap of whichconstitutes The energizing battery 28 is shown connected in one diagonalof the bridge through a variable resistor or rheostat 29 and an ammeter39, whereby the amplitude of deflection of the galvanometer can beadjusted by varying the resistor 29 to vary the total current flowingthrough the bridge and the cells. The galvanometer 3| is connected inthe other diagonal of the bridge.

It is to be understood that the resistors of either the cells l8 and 2|or the cells l9 and 22 could be replaced by fixed resistors, but the useof reference and test cells in all four arms of the bridge in the mannershown increases the sensitivity. 1 The valve I3 is provided tofacilitate balancing of the bridge. Thus by rotating this valve slight-1y counter-clockwise, the test passage l4 can be connected, by the valvepassage l3a, to a branch passage 24a leading to the conduit 24 so thatthe reference gas is passed through both the reference passage 23 andthe test passage l4, and the potentiometer 21 can be adjusted to givezero deflection on the galvanometer 3|. Thereafter the valve l3 can berestored to normal position ,to admit the gas being tested into the testpassage l4. It will be observed that when the passage l3a shaft 39extending forwardly and having a control knob 40 on its forward end.

The valve shaft 39 is extended rearwardly of the valve 38 and connectedto a switch 4|, which is closed when the valve is in the normal positionshown in Fig. 1, but is open when valve 38 is rotated counter-clockwise90. The switch 4| may be the ignition switch of the engine or the powersupply switch of an electric motor driving the suction pump, so that theshifting of the valve 33 occurs simultaneously with stoppage of thepump.

in the instrument panel 46. A removable insert 41 is preferably providedin this instrument panel 46 to facilitate disassembly of the instrument.The rear block 32 may be mounted by screws or bolts, one of which isindicated at 48, to a rear supporting panel 49 positioned back of theinstrument panel 46. The front block 33 is secured to the rear block 32in sealing engagement therewith by a plurality of bolts 59. The conduit5| may consist of a piece of tubing extending is in registration withthe inlet end of the passage H, the passagev l3b connects theconstriction H and the passage l2 with the by-pass passage I4a, whichextends to the exhaust conduit 15 connecting to the inlet of the pumpHi. Therefore, in each operative position of the valve l3, the pump I6is fed with gas through both the constrictions H and 2.").v This insuresthat the same pressure will exist in the cells when balancing the bridgeas when testing a gas.

Thermal-conductivity cells of the general type employed in the system sofar described are well known, and many of the cells already in use canbe adapted for operation in my system. However, I have developed aconstruction of cell that has special advantages, and which is disclosedin Figs. :2 through 5.

Referring first to Fig. 2, there is disclosed a rear block 32 and afront block 33, which together The meter 3| is These resistors 21 and 29have their movable elements coupled by spur gears to control shafts 34and 35, which extend forwardly alongside the meter 3! and terjminate incontrol knobs 36 and 31, respectively. A valve 38 in the suction linemay have a control from the rear block 32 to the junction 26, whichjunction is formed by a single fitting 52 incorporating the valve 39 andadapted to be soldered or welded to the rear block 32.

Referring now to the face view of the rear block 32, shown in Fig. 4,and the sectional view of Fig. 5, it will be observed that the cellchambers for the gas are formed by registering depressions in the rearand front blocks. The passages l4 and 23 are formed completely withinthe rear block 32, both of these passages being of relatively largeuniform diameter from the Y fitting 52 at the lower end of the block toa point adjacent the upper end of the block where they narrow graduallydown to relatively small passages, passage extending directly outof thetop of the rear block 32 and being connected to the conduit 24. Passage23, after being tapered down to a small bore, communicates through thevalve IS with the conduit l2. Both of these conduits 24 and I2 mayconsist of what is commonly referred to as thermometer tubing, which isa flexible metal tubing of substantially 1 mm. internal diameter andarmored with a wrapping of .wire. By employing a small diameter conduitof this type, the block 32 may be mounted many feet from the sources Itand Illa. This greatly facilitates the installation of the apparatus,since the source I9 would ordinarily be positioned closely adjacent theengine of an aeroplane some distance away from the cockpit or cabinwhere the instruments are located. If necessary to prevent condensation,the conduit can be heated, as by enclosing it in, or attaching it to alarger flexible tube through which hot gas such as exhaust gas iscirculated.

The test chambers are formed between the rear and front blocks 32 and33, as shown in Fig. 5. The recesses in the two blocks match in shapeand dimensions, and, as shown in Fig. 4, there are two U-shapedrecesses-the two arms of one of which constitute the chambers l8 and I9,respectively, and the two arms of the other of which constitute thechambers 2| and 22, respectively. The lower part of each U-shaped recessin the rear block is connected by a diffusionpassage with one of thepassages l3 and 23. The diffusion passages are defined by a straightrearwardly extending cylindrical bore which, in this instance is shownto contain a plug 53 having four longitudinally extending grooves 54 inits surface. It is through the passages defined by these grooves .53that the gases diffuse into the chambers l8 and I9, and 2| and 22.

As indicated in Fig. 1, there is a resistor positioned in each of thetest chambers. These resistors are all identical, each consisting of asmall helix of platinum wire 55 (Fig. 5) supported at opposite ends fromlead-in wires 56, which extend through Kovar seals 51 having flanges 58welded or soldered to the margins of bores 59 in which the Kovar sealsare positionedthese bores extending from the front face of the frontblock 33 into the recesses in that block. The Kovar seals form gas-tightelectrically insulating lead-' in structures for the filament-supportingpins 56. The construction described is highly desirable in practicebecause it permits accurate mounting and testing of the platinumfilaments 55, while the front block 33 is removed from the rear block.Thereafter, the two blocks are assembled -and bolted solidly togetherwith the bolts 56.

As is customary in apparatus of this type, it is desirable to maintainthe apparatus at a uniform temperature. To this end, additional recessesare provided in the blocks 32 and 33, which together define cylindricalchannels 60 and 6| for the positioning of a thermostatic switch 62 andan electric heater 63, respectively; these two devices being connectedin series with each other and with an energizing battery 64 through aswitch 65 (Fig. 4). These elements 62 and 63'are of standardconstruction and need not be specifically described herein. Suflice itto say that the thermostatic switch 62 opens the circuit to the heater63 when the temperature of the apparatus exceeds a desired value, andcloses the circuit from the battery to the resistor when the temperaturefalls below the desired value.

It is essential to prevent gas leakage into the test passages andchambers, and it is preferable to employ a construction utilizingmaterials that do not absorb water or other vapors, and that are not aptto form films of materials having low vapor pressure. Thus, although atatmospheric pressure a substance having a vapor pressure of 1 mm. Hg maynot cause sensible error in ordinary apparatus operated at atmosphericpressure, the same substance may cause great error when the total gaspressure is only mm. Hg. This problem is relatively serious, becausewhereas apparatus adapted to operate at atmospheric pressure remains atits operating pressure continuously, the present apparatus working atreduced pressures will often be brought to the reduced pressure only fora. relatively short period of use. Hence, any material capable of givingoff vapor has to be removed before accurate measurements at reducedpressure can be performed.

To eliminate substantially all possibility of leakage into the testcells, I surround the U- shaped recesses in one or both of the blocks 32and 33 with guard grooves 66, each of which is connected by a bore 61 inthe rear block to the associated passage M or 23 at points below thecells. Hence, the space defined by these guard grooves 66 iscontinuously maintained at a pressure at least as low, and possiblylower, than the pressure within the test cells themselves, so that anyleakage of air between the blocks 32 and 33 will, upon reaching theguard rings 66, be drawn of! through the bores 61 before it can reach atest chamber and contaminate the gas therein. It is preferable to takesimilar precautions to prevent leakage of air along the sealing surfacesof the valve I3 to the valve passages by providing annular grooves 68and 69 in the plug of the valve below and above the fluid passagestherein, and connecting these grooves by a passage 16 in the rear blockthrough a T fitting II to the conduit 5| leading to the pump.Longitudinal grooves 12 provided in the valve seat are in constantcommunication with the annular grooves 68 and 69. Since the space withinthe grooves 68, 69 and 12 is maintained at a pressure at least as low asthe pressure within any of the valve passages, there can be no incentivefor leakage of air along the sealing surfaces of the valve to the gaspassages therein.

As best shown in Fig. 4, the marginal portions 14 of the meetingsurfaces of the two blocks are slightly depressed to receive acompressible gasket 15 (Fig. 5), which can be compressed when the bolts50 are tightened, without interfering with.

the close fit of the meeting surfaces immediately adjacent the cellchambers, which surfaces may be ground flat.

It is a relatively simple matter to test for the presence of extraneoussubstances within .the test passages and chambers by varying thepressure therewithin. Thus, variation of the pressure to which the gasesare expanded will not materially affect the deflection of the indicatingmeter as long 'as extraneous vapors or fumeproducing materials areabsent. Therefore, should the reading be found to vary in response to anincrease in the pressure, and there is no leak into the cell, it isdesirable to reduce the pressure to the lowest value obtainable for aninterval of time to accelerate the evaporation and removal of theextraneous material, after which the pressure can be increased to ahigher normal operating value. Variations in the pressure can beobtained by manipulating the valve 36 so as to reduce the rate of flowto the p mp l6 and thereby permit the exhaust gas passing therestriction ll (Fig. 1) to build up a higher pressure in the apparatus.The slight movement of valve 38 required to effect this can be hadwithout opening the switch 4| As has been previously indicated, theapparatus so far described provides for transfer of the gas frompassages I6 and 23 into the test chambers by diffusion through smallopenings provided, in this instance, by the grooves 54 in the plugs 53.It is old to transfer the gas to the test chambers in this fashion atnormal pressures. An important feature of the present invention is themethod of accelerating the migration of the gas between the passages i4and 23 and the associated test chambers by greatly reducing thepressure. However, it is to be understood that the advantages ofoperating at reduced pressure are not limited to apparatus in whichtransfer of gas to and from the cells is effected by diffusion. In fact,the time lag may be reduced even further by positively circulating thegas through the cells at low pressure. The results are less accuratebecause the heat loss by convection is increased, but the convectionlosses are smaller relative to the thermal-conductivitylossesthan theywould be at normal pressures.

It is desirable to make the blocks 32 and 33 of metal because of itsgood heat conducting characteristlcs. A metal should be chosen that isintrinsically corrosion-resistant or it should be plated with a coat ofcorrosion-resistant metal such as gold. It is also possible to employglass in some instances.

- A very important feature of the construction 'within the cells. Byvirtue of the fact that the two blocks contact each other completelyaround the cells, there is no clearance to trap as or liquid. Thus theguard grooves are at the same or lower pressure than the cells andprevent leakage of air into the cells not only because of the pressureconditions that exist but because the composition of the gas in a guardgroove is substantially identical with that in the cell it surrounds.

In my construction, all wiring and adjustment rheostats can be mountedon the front plate and be maintained at uniform desired temperature bythe therm-oswitch and heater. This improves the stability of theinstrument.

Manufacture of the blocks is facilitated by the fact that the front andrear blocks do not need to be made in individually matching pairs.

By virtue of the fact that the guard grooves are, interposed between thecells and the gaskets, the latter can be of any desired material sinceany gases that might be given off by the gasket would be trapped in theguard grooves.

In manufacture, the front blocks containing the filaments can be quicklytested in the factory immediately after their assembly by placing theblOCks against a fixed test block corresponding to the rear block of theinstrument but permanently mounted in the factory for testing purposesonly.

All parts can be readily cleaned and restored to proper operatingcondition, since by removing the front block containing the filamentsand having all the electrical equipment mounted thereon, it can bechecked without disturbing the rear block and the gas lines connectedthereto. the front block removed, the recesses in the rear block areaccessible for cleaning with the rear block in situ. By substituting adummy front block, the passages in the rear block and in the gas linescan be cleaned by flushing them with a solvent, such as carbontetrachloride. However, it is to be understood that cleaning is seldomnecessary when operating at the low pressures I employ.

Heretofore, no attempt has been made to specifically describe'theconstrictions employed to restrict the flow of gas and thereby expandit. Various types can be employed. Thus, it is possible to use a singlevery small orifice, but this is ordinarily objectionable because it mustbe so small that it is subject to clogging. I Another type that may beemployed is a series of orifices, in which case they may be made largerand be less subject to clogging. Where a series of orifices is employed,the pressure drop across each orifice preferably should be at least halfthat across the preceding orifice to prevent back diffusion of the gasin the passage between successive orifices.

Still another constriction that may be employed is a length of capillarytubing, or a capillary tube with a wire in it to further reduce the flowspace. This latter arrangement has the advantage that the wire can bemoved to facilitate cleaning.

With

I cured together.

Referring to Figs. 4 and 5, the rear block 32 is provided with a pair ofdowels projecting from the upper face at -diagonally opposite corners,which dowels are received in registering holes ill in .the outer block33 when the t'wo'parts are se- The dowel pins" not only insure properregistration of the recesses defining the cell chambers, but preventdamage to the filamerits which might otherwise result from bringing thetwo parts together with the recesses out of registration with eachother.

Although for the purpose of explaining the invention, one embodimentthereof has been described in great detail, numerous departures from theexact construction shown will be apparent to those skilled in the art,and the invention is to be limited only to the extent set forth in theappended claims.

I claim:

1. A cell construction for gas analysis by measurement of temperaturechange of a heated filament comprising: a pair of members having closelyfitted surfaces and means for clamping them together, said members beingso configured as to define a filament chamber bounded by said fittedsurfaces, a filament and means supporting it in said chamber and makingelectrical connection thereto, one of said members containing a gaspassage communicating with the filament chamber, means defining a gaschannel connected to said passage for fiow of gas to be tested atsub-ambient pressure, at least one of said fitted surfaces having agroove surrounding said chamber, and means connecting said groove tosaid gas channel at a point therein on the downstream side of said gaspassage.

2. In a gas analysis apparatus including a cell for measurement of thegas: a conduit leading gas to said cell; an operable valve in saidconduit at a point on the upstream side of said cell, said valvehaving'relatively movable mating surfaces; a groove in said matingsurfaces for intercepting leakage of gas from outside into said gasconduit; and a duct extending from said groove to a connection with saidconduit at a point thereon on the downstream side of said gas measuringcell.

3. A cell construction for gas analysis by measurement of temperaturechange of a heated filament comprising: a pair of members so configuredas to define a filament chamber, a filament and means supporting it insaid chamber and making electrical connection thereto, one of saidmembers containing 'a gas passage communicating with the filamentchamber, means defining a gas channel connected to said passage for fiowof gas to be tested at sub-ambient pressure, a valve in said channel onthe upstream side of said passage comprising a seating surface in one ofsaid members, said seating surface and said valve formingcooperatingsealing surfaces and fluid ports, one of said cooperating sealingsurfaces containing annular grooves spaced from said fluid ports, andmeans connecting said grooves to said channel at a point therealong onthe downstream side of said passage.

4. A cell construction of the type describe comprising: a pair ofmembers having closely fitted surfaces and means for clamping themtogether, said members having complementary registering recesses intheir fitted surfaces cooperating to define a filament chambersymmetrical with respect to a plane, the contacting portions of saidfitted surfaces at'opposite ends of'said chamber lying in said plane; afilament-supportplane; a filament in said chamber; and means includingsaid filament-supporting element for supporting said filament in saidplane.

5. A cell' construction for gas analysis by measurement of temperaturechange of a. heated filament comprising: a pair of members havingclosely fitted surfaces and means for clamping them together, saidmembersdefining therebetween a filament chamber; gas-tight lead-.inwires extending through one of said members into said filament chamber;a filament supported by said lead-in wires; one 'of said memberscontaining a gas passage communicating with said filament chamber, andone of said fitted surfaces containing a groove surrounding said chamberand spaced therefrom by a portion of the fitted surface; and means forapplying suction to said groove.

6. An article of manufacture comprising: a member having a recesstherein and having a smoothly finished face surrounding said recess.said face being adapted to fit against a complementary face on anothermember to form a thermal-conductive cell, said member having a groove insaid finished face surrounding said recess, said member having a gaschannel therein for the fiow of gas to be tested and having a passageextending from said gas channel to said recess, said member having asecond gas passage extending from said gas channel at a point lying onthe, downstream side of said first-mentioned gas passage to said groove.

7. As an articlev of manufacture, a section of a gas analysis cellcomprising: a member having a smoothly finished face and having a recessin and completely surrounded by said face; a bare electricallyconducting filament, and means supporting said bare filament in positionextending across said recess in a position spaced from the wall of saidmember; said means consisting of lead-in wires extending through saidmember intosaid recess, said smoothly finished face containing a groovesurrounding said recess.

8.'A cell construction for gasanalysis by measurement of temperaturechange of a heated filament comprising: a pair of members having closelyfitted surfaces and means for clamping them together, said members beingso configured as to define a filament chamber bounded by said \fittedsurfaces, a filament and means supporting it in said chamber and makingelectrical convalve and connecting conduits for selectively in oneposition of said valve connecting one of said supply conduits to onecomparison cell and the other supply conduit to the other comparisoncell, and in the other position connecting said v one supply conduit toboth comparison cells; said valve including means for connecting saidother supply conduit to said suction means in bypassing relationshipwith said comparison cells in said other position of said valve.

10. Apparatus according to claim 9 in which said valve comprises tworelatively movable members having mating-surfaces having cooperatingports therein, one of said members having a first port communicatingwith said one supply conduit, a second port communicating with saidother supply conduit, a third port communicating with said onecomparison cell, and a fourth port communicating with said suctionmeans; the other memberhaving one set of ports for communicating onlysaid first port with said third port in one position of said valve andcommunicating said first port only with said fourth port andcommunicating said second port only with said and a filament supportedby said lead-in wires nection thereto, one of said members containing agas passage communicating with the filament chamber, means defining agas channel connected to said passage for flow of gas to be tested atsub-ambient pressure, at least one of said fitted surfaces having agroove surrounding said chamber, and means connecting said groove tosaid gas channel at a point therein below the point of connection ofsaid gas passage to said gas channel.

9. In a gas analysis apparatus including a pair of comparison cells foranalysis of a pair of gases: a pair of supply conduits adapted forconnection to two different sources of gas and having constrictionstherein for limiting fiow of gases therethrough: suction means fordrawing gases through said supply conduits past um cells; a 10 of saidmember, said points lying on a straight face line that extends throughportions of said at opposite ends of said recess.

wLAnmm M.ZA1KOWSK.Y. I

REFERENCES CITED The following references ares: record in the file ofthis patent:

v UNITED STATES PATENTS Date Number Name 1 1,436,084 .Hamlin Nov. 21.1922 1,954,681 Oetjen Apr. 10, 1934 2,013,998 Goldsborough Sept. 10,1936 2,211,627 Morgan et ai. Aug. 13. 1940 2,269,850 Hebler Jan. 13,1942 FOREIGN PATENTS.

Number Country Date June 14, 1938

1. A CELL CONSTRUCTION FOR GAS ANALYSIS BY MEASUREMENT OF TEMPERATURECHANGE OF A HEATED FILAMENT COMPRISING: A PAIR OF MEMBERS HAVING CLOSELYFITTED SURFACES AND MEANS FOR CLAMPING THEM TOGETHER, SAID MEMBERS BEINGSO CONFIGURED AS TO DEFINE A FILAMENT CHAMBER BOUNDED BY SAID FITTEDSURFACES, A FILAMENT AND MEANS SUPPORTING IT IN SAID CHAMBER AND MAKINGELECTRICAL CONNECTION THERETO, ONE OF SAID MEMBERS CONTAINING